Animate wireframe slider Blender 2.8
Not with keyframes or drivers

The overlay is a member of the 3d view space. bpy.types.SpaceView3D  Each property in blender has an is_animatable property, declaring if it can be animated.  Visually if you right click and there is no add driver or insert keyframes

Step thru this in the python console where C = bpy.context

Find which area is the 3d view

&gt;&gt;&gt; for i, a in enumerate(C.screen.areas):
...     i, a.type
...     
(0, 'PROPERTIES')
(1, 'CONSOLE')
(2, 'VIEW_3D')
(3, 'TEXT_EDITOR')

&gt;&gt;&gt; a = C.screen.areas[2]


Its 3d view space will be the active one

&gt;&gt;&gt; s = a.spaces.active


And here is the overlay wireframe threshold

&gt;&gt;&gt; s.overlay.wireframe_threshold
0.0


Let's see if the property def says it is animatable.

&gt;&gt;&gt; p = s.overlay.bl_rna.properties['wireframe_threshold']
&gt;&gt;&gt; p.is_animatable
False


Confirmed ... Nope.

There are some dodgy ways this could be achieved, but will wait for further details on animation required to elaborate.